Conventional solenoid controlled hydraulic valves have solenoid coils mounted externally of the valve body. The solenoid is connected with the internal parts of a valve by two distinctive methods:
air gap solenoids have an armature working against a pushpin which is dynamically sealed against leakage of fluid from the valve body;
wet pin solenoids have a coil encircling non-magnetic tubing with a slidably disposed armature, the tubing being internally exposed to system pressure.
There are well recognized disadvantages in both structures. The dynamic seals of the air gap solenoids are not reliable, create substantial friction forces, and limit the valve operating pressure. The non-magnetic tubing of wet pin solenoids creates substantial resistance to magnetic flux and also limits the valve operating pressure. In both configurations the solenoid coils are located on the exterior of the valve body and dissipate heat to the surrounding environment. As a result, solenoid coils of conventional valves have a winding of excessive size and are costly when compared with other valve components.
Consider, in particular, the poppet type solenoid controlled hydraulic valves. The limitations of these type valves can be outlined as follows. Poppets slide within a valve body. Their position is controlled by either internal or external pilot pressure. Valves with internal pilot lines can operate only if the clearance between the slidable poppet and the adjacent valve member is extremely small. This relationship is required in order to control the differential pressure on opposite sides of the poppet. Such closeness of clearance requires very fine machining tolerances and surface finishes of the poppets and adjacent components. These requirements also limit the size of poppet valves having internal piloting since leakage across the poppet becomes uncontrollable with increasing by larger dimensions. One can conclude (with poppet valves having external piloting) that because of the leakage across the poppet body from the pressure line to the pilot line, that these valves cannot be used for applications where internal leakage is not allowed. Further, external pilot sections are actually additional valves with all their complexity and cost.
It is, therefore, an object of the present invention to provide a valve structure where the pilot controlling section is disposed within the valve body immediately adjacent to the main section of the valve and thus, providing a compact structure with a minimum for potential external leakage points and a faster response time.
Another object of the present invention is to provide a solenoid hydraulic valve structure where the solenoid coil is fully integrated with other valve components, by positioning the solenoid coil inside the valve body and exposing the coil to the pressurized fluid. This integration of the electromagnetic coil within the valve body, as disclosed in the present invention, permits construction of the magnetic circuit with practically no detrimental gaps. This construction utilizes the coil electromagnetic forces to their greatest potential.
Another object of the present invention is to provide a solenoid valve structure where the solenoid coil is positioned within the valve body in such a way that the coil contact with the surrounding atmosphere is eliminated making valves constructed in accordance with the present invention capable of operating in hazardous environments.
Another object of the present invention is to provide a solenoid controlled pilot operated valve structure which consists of a main section and a number of pilot sections located closely adjacent the main section in a common valve body constructed in such manner that the main valve section may accomplish different functions according to the pilot section which is actuated. For example the function may be: normally-open or normally-closed directional control, pressure relief, flow check, etc.
Another object of the present invention is to provide a solenoid controlled, pilot operated, poppet type valve structure where the main valve member is slidably sealed by a novel adjustable seal-bearing comprising a deformable plastic sleeve circumferentially mounted over a tapered portion of the main valve member abutting an adjusting nut. Under pressure from the adjusting nut the plastic sleeve moves along the tapered portion expanding to such degree that it fills the clearance between the main valve member and the mating body component of the valve. This creates a minimum friction seal and plain bearing, simultaneously, with leakage reduced to nothing. This greatly reduces requirements for machined finishes and tolerances of principal valve components.
Another object of the present invention is to provide a solenoid controlled valve structure where the solenoid coil is positioned within the valve body chamber and integrated with other valve components in a manner which allows the coil to be cooled by circulating hydraulic system fluid about the coil. Direct contact of coil with system circulating fluid radically improves heat dissipation efficiency.
Other objects and advantages of the present invention will become apparent from the following detailed description.